Light emitting diodes (LEDs) have been used for decades in applications requiring relatively low-energy indicator lamps, numerical readouts, and the like. In recent years, however, the brightness and power of individual LEDs have increased substantially, resulting in the availability of 1 watt and 5 watt devices.
while small, LEDs exhibit a high efficacy and life expectancy as compared to traditional lighting products. A typical incandescent bulb has an efficacy of 10 to 12 lumens per watt, and lasts for about 1,000 to 2,000 hours; a general fluorescent bulb has an efficacy of 40 to 80 lumens per watt, and lasts for 10,000 to 20,000 hours; a typical halogen bulb has an efficacy of 20 lumens and lasts for 2,000 to 3,000 hours. In contrast, white LEDs can emit 100 lumens per watt with a life-expectancy of about 100,000 hours.
The light engine of an LED lamp typically includes a high thermal conductivity substrate, an array of individual LED semiconductor devices mounted on the substrate, and a transparent polymeric encapsulant, e.g., optical-grade silicone, deposited on the LED devices.
The LED must maintain its junction temperature in the proper rated range to maximize its efficacy, longevity, and reliability. Accordingly, the construction of the light engine must provide for dissipation of the heat generated by the LEDs. High-power LED lights are housed within finned fixtures, for example. The fins dissipate the heat to ambient surroundings.
In general, LED lamps provide a high-efficiency light source, but due to their construction do not provide the same light output characteristics as conventional light sources. For example, unlike typical omni-directional incandescent or fluorescent lamps, the illumination pattern of LEDs tends to be directional, like that of a floodlight, down light, spot light or task light. Accordingly, light engines formed with LEDs tend to generate high-intensity and one-half spherical beams of light. As such, LED lamps are not light sources for illuminating a room, office, or other space as an incandescent lamp does by emitting light fully spherically. Because LEDs themselves are directional lighting devices, it is difficult to manufacture an omni-directional LED lamp.